Police stand by at the crime scene on Raymond Avenue April 11. (Alan Mittelstaedt/Neon Tommy)

A key witness in the February shooting linked to the murders of two USC graduate students told police he could identify the gunman nearly two months before Wu Ying and Qu Ming were killed, court documents show.

The two Chinese electrical engineering students were gunned down April 11 around 1 a.m. inside a double-parked BMW on South Raymond Avenue, less than a mile from campus. Within hours, Los Angeles Police Department investigators had matched shell casings found at the scene to two other South L.A. shootings—one on Dec. 3, 2011 and another at a birthday party Feb. 12.

Police retraced their steps in the February investigation to quickly identify 20-year-old Bryan Barnes as a primary suspect. Barnes and his accused accomplice, 19-year-old Javier Bolden, were arrested May 18 and are scheduled to enter pleas Monday in Los Angeles Superior Court on charges related to the three shootings.

UPDATE: Barnes and Bolden's arraignment has been postponed until July 18.

A Neon Tommy exclusive report earlier this month provided details of detectives’ interview with a witness to the February shooting. During their April 11 meeting, the witness used a department computer to pull up Barnes’ Facebook page and exclaimed, “That’s him! That’s the guy that shot [one of the Feb. 12 victims]."

The interview took place within 20 hours of the USC students’ murders and was a major break in the case. But the latest batch of search warrants obtained by Neon Tommy shows the witness in fact told detectives two months earlier he could identify the gunman who opened fire at the Feb. 12 party.

Deputy Chief Pat Gannon of the Southwest Division said he might have handled the February investigation differently. “I think the appropriate thing to do is to try to work with that witness as best you can to help identify the person,” he said.

“If it was me, I’d want to somehow secure the information off of Facebook. [The tip] is important, absolutely important, but you have to have some corroborating evidence,” Gannon continued. “In most cases, you like to have two or more witnesses that can identify your suspect.”

It’s unclear how vigorously police pursued the tip from the witness. Details in warrants filed Feb. 23 and March 29 outlined a different route in their investigation.

Those warrants ordered Metro PCS and Sprint Nextel to produce phone records for two numbers dating back to Dec. 3—the same night 20-year-old Timothy Hall was shot at a party in South L.A. Ballistics testing has since tied the December shooting to Barnes and Bolden, though police won’t say when they made the connection with the shooting at the February birthday party.

The search warrants include details about the birthday party and the aftermath of the shooting. Police, responding to radio calls of an “ADW Shooting”—assault with a deadly weapon—arrived at a party rental hall near the intersection of 51st Street and Western Avenue in the early hours of Feb. 12.

Officers found 21-year-old Deionce Davance shot twice in the head and several times in the stomach. Another partygoer, Zanae Flowers, had been shot in the right calf. Both were taken to a nearby hospital for treatment. Davance is now paralyzed.

Detective Erbie Phillips of the LAPD’s 77th Street Community Division got the case the next day.

The warrants detail Phillips’ Feb. 13 meeting with the witness who would later identify Barnes. “Later that day, [the witness] came to 77th Station and met with Affiant. [The witness] advised he was standing with [Davance] when he was shot. [The witness] advised he knows who the shooter is because he located a picture of the shooter on Facebook.”

But the reports do not say what detectives did with the information. Instead, Phillips’ account jumps ahead to Feb. 20, when he used phone numbers provided by party guests to track down a man named “K witt it,” the promoter responsible for the party at 5117 S. Western Ave.

According to the warrants, Phillips called and spoke briefly with a man who claimed to be K witt it. When pressed for his legal name, the man hung up and did not answer the phone again.

Police requested phone records for K witt it and a party guest to help determine “who attended the party and possible location of alleged suspect or suspects,” Phillips’ reports read.

The Feb. 23 warrant was not served, but Metro PCS produced records sought in the March 29 warrant by April 9—two days before Ying and Ming were killed.

Deputy Chief Gannon said he didn’t see a reason detectives would choose to sit on the information provided by the witness in February. “No, no. That’s an important piece,” he said. “Here, I’m really speculating on that, but I don’t want to downplay it.”

The reports do not include what follow-up questions, if any, detectives may have asked the witness when he said he could identify the gunman on Facebook. Did Phillips, for example, ask him to call up Barnes’ profile so he could see his name and other identifying information?

“You know, he may have,” Gannon said. “It just may not be included in that information you have.” He explained detectives also keep a chronological record of their work that often includes details beyond those in a warrant’s report.

Whatever might be in Phillips’ record, Gannon openly shared his concerns that more aggressive work on the December and February shootings could have prevented tragedy in April.

“Not every case gets solved really, really quickly,” Gannon said. “I wish it wasn’t that way. And I wish in hindsight that we had tied those first two cases together, and that we did have Barnes and Bolden in custody. Maybe if that had been the case, these two young people from USC would never have been killed. That’s a burden—for me and for the investigators to carry with us. But I just don’t want anybody to think it’s for lack of trying.”

The USC students’ murders and the two earlier shootings are now being handled by Criminal Gang Homicide Division detectives Vince Carreon and Eloy Ochoa. When reached by phone, Carreon repeated the District Attorney’s instructions not to address specifics of the investigation. “I can’t really give you much—or anything really,” he said Thursday, “because of the seriousness of this case.”

Carreon also said the arraignment for Barnes and Bolden wouldn’t loosen restrictions on what he can say. “It will have to come out in trial.”